Project Summary Cell therapy is promising for repair of damaged myocardium. But moderate and variable functional benefits in clinical trials emphasize the need for a better understanding of therapeutic mechanisms and for specific imaging techniques which provide insights beyond cardiac function. Frequently, only a small fraction of transplanted cells engrafts in injured myocardium, limiting therapeutic efficacy and providing a potential explanation for the variability of functional benefits. The myocardial microenvironment is considered to be a critical contributor to successful cell engraftment and constitutes a suitable target for molecular imaging. In this proposal, we aim at developing strategies to facilitate successful stem cell engraftment. Our central hypothesis is that molecular-targeted nuclear imaging prior to cell delivery can characterize an optimal biologic environment which is supportive of cell engraftment after delivery, and thus predictive of successful myocardial regeneration. This hypothesis will be tested in 3 specific aims. Quantitative nuclear imaging techniques will be employed to characterize both, myocardial environment, as well as stem cell engraftment in a rat model of myocardial infarction. Therapy outcome will be defined by serial echocardiography and histologic workup. Aim 1 will define the role of tissue perfusion, metabolism and viability in the target area of stem cell delivery, for successful engraftment of cardiac-derived stem cells, an innovative cell type with documented regenerative potential. Aim 2 will investigate the role of expression of the adhesion molecule 1v23 integrin in the target area, as determined by molecular imaging, for successful cardiac stem cell engraftment. In aim 3, cardiac stem cells as a newer cell type will then be compared with the longer established mesenchymal stem cells under conditions of optimal imaging-defined microenvironmental conditions. These studies will provide unique new insights into the contribution of the biologic environment to the success of stem cell based myocardial regeneration. More importantly, they will also provide imaging techniques which may assist in therapeutic decision making by guiding the timing and regional targeting of cell delivery. The ultimate goal of the project is to optimize cell therapeutic benefit based on imaging of individual disease biology.